Oxidative dehydrogenation of ethane to ethylene in a system with circulating microspherical metal oxide oxygen carrier: 1. Synthesis and study of the catalytic system

Article abstract of DOI:10.1134/S0965544115080125

By screening a large series of oxide systems, the most effective modified Mo catalysts for oxidative dehydrogenation of ethane to ethylene with selectivity for the desired product of more than 90% have been found. Using TG-DTA and XRD techniques, it has been shown that the state of the support (Al₂O₃) determines the formation of active sites. The procedure for preparing microspherical Mo catalysts is characterized by simplicity and complete reproducibility of their properties. Further investigation in this line is associated with testing a pilot batch of the Mo catalyst on a pilot unit with a riser reactor.

Full text of DOI:10.1134/S0965544115080125

ISSN 0965ꢀ5441, Petroleum Chemistry, 2015, Vol. 55, No. 8, pp. 651–654. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © S.N. Khadzhiev, N.Ya. Usachev, I.M. Gerzeliev, E.P. Belanova, V.P. Kalinin, V.V. Kharlamov, A.V. Kazakov, S.A. Kanaev, T.S. Starostina, A.Yu. Popov, 2015,
published in Neftekhimiya, 2015, Vol. 55, No. 6, pp. 506–509.
Oxidative Dehydrogenation of Ethane to Ethylene in a System
with Circulating Microspherical Metal Oxide Oxygen Carrier:
1
. Synthesis and Study of the Catalytic System
a
b
a
b
b
b
S. N. Khadzhiev , N. Ya. Usachev , I. M. Gerzeliev , E. P. Belanova , V. P. Kalinin , V. V. Kharlamov ,
b
b
b
a
A. V. Kazakov , S. A. Kanaev , T. S. Starostina , and A. Yu. Popov
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
a
eꢀmail: gerzeliev@ips.ac.ru
Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia
b
eꢀmail: ny@ioc.ac.ru
Received June 29, 2015
Abstract—By screening a large series of oxide systems, the most effective modified Mo catalysts for oxidative
dehydrogenation of ethane to ethylene with selectivity for the desired product of more than 90% have been
found. Using TG–DTA and XRD techniques, it has been shown that the state of the support (Al O ) deterꢀ
2
3
mines the formation of active sites. The procedure for preparing microspherical Mo catalysts is characterized
by simplicity and complete reproducibility of their properties. Further investigation in this line is associated
with testing a pilot batch of the Mo catalyst on a pilot unit with a riser reactor.
Keywords: ethane, ethylene, oxidative dehydrogenation
DOI: 10.1134/S0965544115080125
Lower olefins are basic feedstock for the producꢀ
Gerzeliev et al. [1, 2] formulated the concept of
tion of various petrochemical products (polymers, partial oxidation of lower alkanes to synthesis gas by
functional plastics, alkylating agents, hetero comꢀ active lattice oxygen of metal oxide systems in a pilot
pounds, etc.). Oxidative dehydrogenation of ethane unit with a riser reactor. This approach is applicable to
(
ODE) is probably the most promising for ethylene ODE as well, since it suggests separate ethane feeding
production as compared with conventional processes. onto the oxide system followed by regeneration of the
However, there is still no even a pilot unit for selective reduced catalyst with air oxygen. This arrangement
ODE, although the solution of this problem can elimꢀ makes it possible to avoid the formation of explosive
inate many of the disadvantages of the pyrolytic proꢀ ethane–air mixtures, improve ODE product selectivꢀ
cessing of various hydrocarbons (high consumption of ity, and additionally obtain technical nitrogen at the
energy required for feedstock cracking, catalyst cokꢀ catalyst regeneration step. The separate contact of
ing, formation of a considerable amount of byprodꢀ ethane and air with the fixedꢀbed oxide system is
ucts, etc.).
attainable in two separate devices, the reactor and the
regenerator. In this case, there are technological comꢀ
plications associated with the switching of ethane and
air streams and the need to remove hydrocarbons and
air with an inert gas from the reactor and the regenerꢀ
ator before switching the flows. A reactor that provides
circulation of a microspherical catalyst between the
reaction and regeneration zones (Fig. 1) is free of these
drawbacks. Ethane is fed into the bottom of the flow
riser reactor, in which ODE occurs on the catalyst that
arrives from the transport line of the regenerator and
oxidizes ethane. The reduced catalyst is regenerated
by atmospheric oxygen and then recycled to the reacꢀ
tor, ensuring rapid oxidation–reduction cycling.
Oxidative dehydrogenation of ethane is an exotherꢀ
mic reaction that occurs at a relatively low temperaꢀ
ture and atmospheric pressure:
→
C H + H ,
4
2
C H6
2
2
H +
2
½
O2
→
H O,
2
C H +
2
½
O2
→
C H + H O.
2 4 2
6
It should be noted that there are various embodiꢀ
ments of ODE. The first of them suggests the simultaꢀ
neous supply of ethane and oxygen (air) to the reacꢀ
tion zone. This creates a dangerous situation and leads
to dilution of the products, for example, with nitrogen.
Moreover, the presence of gaseous oxygen in the reacꢀ
Various systems capable of mediating the selective
tion zone results in occurrence of uncontrolled gasꢀ dehydrogenation of С –С4 hydrocarbons have been
2
phase reactions, which decrease the ODE selectivity.
proposed to date. The mixed oxides that are most freꢀ
651

652
KHADZHIEV et al.
EXPERIMENTAL
N2
Catalyst Preparation and Testing
The catalysts were prepared by impregnating
microspherical alumina samples (50–160 m), which
were in the and ꢀforms. In the first step, the microꢀ
spheres were impregnated with an aqueous solution of
NH ) Mo O 4H O. After drying at 100 for 2 h,
the resulting material was impregnated with a modifier
solution and dried at 100 again to constant weight.
The final step of catalyst preparation was its calcining
at 600 for 2 h and at 100 for 2 h.
μ
α
ꢀ
γ
C H + C H + CO
x
2
4
2
6
(
⋅
°С
4
6
7
24
2
°
С
°С
°С
Catalyst samples were tested in the pulse reactor
described in [21]. Product analysis procedures and
formulas for calculating the conversion of ethane and
selectivity for ethylene, methane, and carbon oxides
are also given in [21].
C H
2
6
Thermal Analysis of Catalysts
The thermal properties of the initial components
and oxides were studied using a DerivatographꢀC
instrument (MOM, Hungary) in alundum crucibles
with programmed heating (10°C/min) in an air atmoꢀ
sphere. The weight of specimens was 20–30 mg. The
Air
Fig. 1. Schematic of the pilot plant with a circulating carꢀ
rier of lattice oxygen for oxidative dehydrogenation of
ethane in the continuous mode.
reference material was ꢀAl O3.
α
2
Xꢀray Diffraction Analysis of Catalysts
quently used contain Mo, V, Te, Nb, Sn, or Ti supꢀ
The Xꢀray diffraction (XRD) study was performed
on a DRONꢀ3M Xꢀray diffractometer (radiation Cuꢀ
ported on Al O [3–19]. In papers [4, 9] concerning
2
3
the synthesis of Mo–V–Te–Nb–O catalysts, it was
noted that certain conditions for the preparation of
oxide systems need to be strictly observed, with the
complexity of the procedure being due to the hydroꢀ
thermal synthesis step of the formation of a highly
crystalline phase of defined composition and strucꢀ
ture. Another problem is caused by the need to obtain
a shaped catalyst, into which a crystalline phase of this
kind is to be introduced.
Kα
, Ni filter) at a scan rate of 1 deg/min in the
2θ
angle range of 5°–75°. XRD data were obtained by
processing the spectra by the Rietveld method using
the program RIETANꢀ2000 [22]. The particle size was
evaluated by the halfꢀwidth of the peaks using the
Scherrer equation.
RESULTS AND DISCUSSION
Physicochemical and Catalytic Properties
It should be pointed out that the systems used as
oxygen carriers exhibit catalytic properties in the presꢀ
ence of gaseous oxygen as well, with the reaction folꢀ
lowing the Mars–van Krevelen mechanism in this
case. However, the presence of О2 in the gas phase
leads to severe oxidation of the reaction olefins, as
shown for the 20 wt % Al O catalyst as an example [3].
of Microspherical Samples Based on
The thermal study showed that the starting alumina
is in the ꢀform. The mass loss ( ) in the range of
0–600 is as low as 0.2%. The very low moisture
α
ꢀAlumina
α
Δm
2
°С
content of this sample is consistent with the XRD
spectrum, which exhibits reflections corresponding
fully to the corundum phase. This may explain the low
2
3
In view of the importance of solving the problem of activity of the sample in the temperature range
oxidative dehydrogenation of lower alkanes with the (Table 1), since its small surface area prevents uniform
participation of lattice oxygen, intensive studies aimed distribution of the active phase.
at optimizing both the composition of oxide systems
and their preparation procedure are continuing in
The nature of interaction between MoO3 and
ꢀAl O3 in the MoO3/ ꢀAl O3 sample can be judged
α
α
2
2
many research centers. The results obtained enable the by its XRD spectrum (Fig. 2). It can be seen that the
preparation of modified highꢀperformance Mo sysꢀ reflections due to the
ꢀAl O3 phase are completely
tems, which form the basis for the development of a retained. Highꢀtemperature treatment (800
microspherical oxygen carrier for the oxidative dehyꢀ stantially inactivates the MoO /Al O sample
α
2
°С) subꢀ
3
2
3
drogenation of ethane to ethylene in the circulating (Table 2). Thus, it can be concluded that for the
mode using a riser reactor. MoO /Al O system to have activity in ODE, it is necꢀ
3
2
3
PETROLEUM CHEMISTRY Vol. 55
No. 8
2015

OXIDATIVE DEHYDROGENATION OF ETHANE TO ETHYLENE
653
Table 1. Conversion of ethane over 5% MoO /Al O (
α
ꢀalumina microsphere). Three feed pulses at each temperature
Selectivity, %
3
2 3
Ethane
conversion, %
Catalyst
T, °C
C H
CH4
CO
CO2
2
4
2
.5
50.9
46.4
53.5
72.7
74.0
72.4
74.9
75.2
74.0
0
0
0
0
0
0
0
0
0
39.3
45.1
38.8
22.3
22.1
22.6
18.5
18.4
19.9
9.8
8.5
7.7
5.0
3.9
5.0
6.6
6.4
6.1
500
3.1
2
.6
.0
7
5
%MoO3/
α
ꢀAl O3
2
(
impregnation of microsphere)
550
6.3
.1
7.8
13.5
1.8
6
1
600
1
Table 2. Conversion of ethane over a MoO /Al O sample (
α
ꢀalumina microsphere after calcination at 800
Selectivity, %
°
C, 1 h). Fives
3
2 3
feed pulses
Ethane
Catalyst
T
, °C
conversion, %
C H
CH4
CO
CO2
2
4
MoO3/
Calcined at 800°C
α
ꢀAl O (microsphere)
600
1.7
44.2
49.7
46.4
50.6
44.2
0
0
0
0
0
23.2
18.7
26.5
24.1
23.2
32.6
31.6
27.1
25.3
32.6
2
3
1.8
1.1
1.3
1.2
essary that the Mo component be quite evenly distribꢀ duced are in the finely divided (Xꢀray amorphous)
uted on the support surface.
state.
All of there findings, including the data on high
selectivity (>90%) of modified MoO /Al O prepared
from Al(OН)3, show the determining role of the state
of the support of Mo components (Table 3).
3
2
3
Physicochemical and Catalytic Properties
of Microspherical Samples Based on
γ
ꢀAlumina
The procedure for preparing Mo catalysts is simple
and ensures complete reproducibility of their properꢀ
According to the thermal analysis data, the starting
ꢀalumina contains 9 wt % adsorbed substances,
γ
which are removed in the temperature range of 20–
8
00
bands characteristic of alumina in the
its low crystallinity. After deposition of the modifier
crystal hydrate, the mass loss in the range of 20–440
°
С
. The XRD spectrum of this sample has broad
I
γ
ꢀform, showing
°С
is about 32%, which is probably due to the removal of
adsorbed water and the decomposition of the crystal
hydrates of the salts. This process is accompanied by a
substantial absorption of heat with an extremum at
100°C.
Note that the XRD spectrum (Fig. 3) of the
γꢀaluꢀ
mina sample after its treatment with ammonium hepꢀ
tamolybdate and the modifier followed by calcination
10
20
30
40
50
60
70
80
, deg
2
θ
for 1 h at 600°С does not exhibit any reflection that
can be attributed to the deposited components. This
feature is direct evidence that the components introꢀ
Fig. 2. Xꢀray diffraction spectrum of initial alumina in the
ꢀform.
α
PETROLEUM CHEMISTRY Vol. 55
No. 8
2015

654
KHADZHIEV et al.
I
10
20
30
40
50
60
70
80
, deg
2
θ
Fig. 3. XRD spectrum of a sample of alumina in the
γ
ꢀform after deposition of ammonium heptamolybdate and the modifier crysꢀ
tal hydrate followed by calcination for 1 h at 600°C.
Table 3. Oxidative dehydrogenation of ethane to ethylene on the modified microspherical catalyst MoO3/
γ
ꢀAl O . Three
2
3
feed pulses
Selectivity, %
Ethane conꢀ
Catalyst
T, °C
version, %
C H
CH4
CO
CO2
2
4
4
4.4
96.7
96.7
94.5
0.06
0.3
2.1
2.0
2.4
1.14
1.0
Modified microspherical catalyst
600
39.2
MoO3/ ꢀAl O
γ
2 3
6
6.5
0.7
2.4
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1
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ing a pilot batch of the microspherical Mo catalyst in a
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1
1
1
1
1
1
1
2. R. Q. Solórzano, R. S. RuizꢀMartínez, and C. Castilloꢀ
ACKNOWLEDGMENTS
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The work was supported by the Ministry of Educaꢀ
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no. 14.607.21.0054 (applied research unique identifier
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Translated by S. Zatonsky
PETROLEUM CHEMISTRY Vol. 55
No. 8 2015